Mind games:
1. Giving your opponent a different 'look' when they are expecting a specific reaction.
example -> Rather than doing an F-tilt, or U-Tilt, you do a Down-Tilt to refresh the move queue.
2. Conditioning your opponent to react to a stimulus the same way so you can take advantage of it later.
example -> Every time your opponent is recovering off stage, you edge hog. They then assume that they need to recover high every time and that you are passive. This then sets up an easy Bair/Fair/Nair/u-tilt later in the game when you need to finish them.
3. Repetitive Move use to frustrate.
example -> Every time your opponent attacks, you grenade counter. Their approach slows down, and you are able to exploit.
4. Tech chases.
Example -> Down throw. If you can get it to where you can predict your opponent for six throws, you're going to destroy their mentality.
5. False approaches.
Example -> You cautiously move forwards towards your opponent. Prior to entering F-Tilt range, you instead dash the other way into a mortar slide. If the opponent chases, they'll be hit.
6. Prediction of defense.
Example -> Your opponent constantly spot dodges your attacks. Instead of doing an F-tilt, you go into a Dash grab, or a slightly charged F-Smash.
7. False Traps.
Example -> Placing a C4 at the middle of the stage that you have no intention of detonating every time you can. Eventually, you detonate it when they are ontop of it after they ignore it completely.
I could go on, but I'm at work.
In competitive gaming, I tend to go with the rule of three. I can assume that after doing a move three times, that my opponent is going to have come up with a suitable counter measure or will change their behavior to cope with what I've done.
First use -> Observation.
Second use -> Pattern found.
Third use -> Change of behavior/counter found.
Most of my mind games are based off of this, and it does wonders. I then even use the 'three count' as a mind game, since I'm forcing them through their progression to a counter/change of behavior.